I use Ambient Shadows:SSAO24r as an automatic calc. I consider ambient shadow to be a minimum requirement for seeing any depth in a render.
Anything else is calculated after I have rendered and saved a 1:2 anti-aliased image file and the M3I file.
I can then reopen the M3I file, add Postprocess effects and save a new image file. DOF calc time is usually short so I use it more often.
Hard Shadows and/or Reflections are calculation intensive so I rarely use them. When I do, I blend the Ambient Shadow image with the separate Hard Shadows and/or Reflections image in Photoshop using layers.
haha - okay, you're perfectly pro I just wanted to encourage you to use more or more intense shadows - but that's obviously just my taste and if you think it's a not so good idea to bother an artist with personal taste proposals I even would agree ...